Air separator

ABSTRACT

Air separator with cylindrical housing for the separating chamber and with an inwardly located radial impeller, in which a plurality of outwardly located cyclones are, by means of entrance passages, arranged behind the radial impeller in such a way that the direction as well as the magnitude of the absolute exit velocity of the separating air will when entering the entrance passages not be subjected to any change.

O Unlted States Patent 1131 3,682,302

Bernutat 1451 Aug. 8, 1972 1541 AIR SEPARATOR I 3,095,369 6/1963 Jager ..209/139 R 3,483,973 12/1969 J'ager..... ..209/139 R [72] {33 fig m 3,520,407 7/1970 Rumpf m1. ..209/139 R y 3,524,544 8/1970 lager ..209/139 R x 22 Filed: March 2, 1970 [21] A l N 15495 FOREIGN PATENTS 0R APPLICATIONS 455,177 2/1950 ltaly., ..209/144 [30] Foreign Application Priority Data Primary Examiner-Frank W. Lutter Assistant Examiner-Ralph J. Hill March 1, 1969 Germany ..P 19 10 501.2 Ammy waher Becker 52 US. Cl ......209/139 R, 209/144, 5 5 /3 43 [57] ABSTRACT 51 1111. 01. B071 4102 A separator with qy 9 housing for the ep r [58] FieldoiSearch..209/l39 R, 144, 150, 211, 154; 8 a with an 9 located radlal 510/212; 55/343, 347, 349, 450, 459, 396, Pellet, which a plurality of outwardly Owed 340 cyclones are, by means of entrance passages, arranged behind the radial impeller in such a way that the "was direction as well as the magnitude of the absolute exit [56] Ref Cm velocity of the separating air will when entering the UNITED STATES PATEN'IS entrance passages not be subjected to any change.

2,858,020 10/1958 Bfik ..209/211 6Clalms,2lkawingflgures AIR SEPARA'DOR The present invention relates to an air separator in which the air containing fine material has the dust removed therefrom in cyclones which are arranged outside the separator chamber, and in which the fan which produces the air flow is located within the separator.

Air separators are known according to which the air containing the fine material to be separated has the dust withdrawn therefrom in cyclones, said cyclones being located outside the separator chamber, and in which the fan producing the air flow is located not within the separator but likewise outside the same. The charging of the material to be separated into the separating chamber is effected by means of a scattering dish. The foremost drawback of this heretofore known air separator consists in that the separating power of the cyclones is not constant. The reason for this fact lies in that the air flow circulating between the separator and the fan has to be varied in conformity with the respective desired fineness of the sifted material. This variation of the quantity of air to be circulated is obtained by a change in the resistance in the separator. This, however, means that the supply of air containing the fine material to the cyclones varies to the same extent, and consequently also the diameter of the separated granules varies in the material sifted by the cyclones. Inasmuch as the end drop velocity of the separated granules will with a given cyclone be inversely proportional to the passed through quantity of air, the separating power will change with the respective fineness of the separated material in such a way that with increasing fineness of the separated material, i.e. with decreasing air velocity in the separator, the separating power of the cyclone decreases more and more. The separating air which flows from the cyclone back into the separating chamber thus contains a major portion of fine material. It is due to this fact that one on hand the degree of separation decreases in view of the air carrying more and more fine material into the separating chamber (it is a well known fact that with increasing fineness of the material to be separated the degree of separation drops considerably), and on the other hand it is necessary that the quantity of the material to be separated and charged into the separator must be reduced by the amount which corresponds to the recirculated proportion of the fine material inasmuch as for each degree of fineness of theseparated material the specific dust content in the separating chamber (at a predetermined air velocity) must not exceed a certain value. The range in which the circulated quantities of air and thereby the separating power of the cyclones vary is relatively high. The degree of fineness of the separated material expressed by its specific surface is approximately inversely proportional to the root of the circulated quantity of air. It is necessary that this fineness be varied with industrial separators from 2,000 to 5,000 cmlgr. The end drop velocities of the granules having the separating grain diameter in the cyclones have a ratio of approximately 6 1 with regard to the upper and lower limit of the adjusting range.

A further drawback of the heretofore known air separators consists in the relatively high power consumption. This high power consumption is caused by the non-variable resistances which are inherent to the separator construction and which have to be overcome by the separating air flow, and is furthermore caused by the variable resistance by means of which the axial velocity of the separating air in the separating chamber, i.e. the circulated quantity of air, is brought to the value which results in the respective desired fineness of the separated material.

The non-variable resistances are found in the collecting line between the cyclones and the fan, in the line between the fan and the separator, and in the separator itself where the resistance is due primarily to the connection of the cyclone passages to the housing for the separating chamber. Inasmuch as the total of the rectangular cross-sections of the connections of the cyclones amounts to only a fraction of the cross-section of the separating chamber, the separating air containing the fine material will, when entering the cyclone passages, undergo an increase in its velocity which increase corresponds to the said ratio of the cross-sections. The acceleration inherent to this increase in velocity causes a pressure loss which is composed of the pressure loss for accelerating the pure separating air and in particular the pressure loss for accelerating the fine material in the separating air. Also by a tangential connection of the cyclones to the separating chamber, this pressure loss is only slightly reduced.

The variable resistance is produced by a change in the speed of a so-called counter impeller which is arranged above the scattering dish and which is used also with air separators with inner impeller for changing the circulated quantity of air. With an air separator having an outside fan, the counter impeller which with its blades adjusted to a certain pitch angle practically works like a counter running axial impeller, will in conformity with its infinitely variable speed cause a certain resistance which has to be overcome by the separating air passing through the separator. The change in the circulated quantity of air brought about in this manner results in a particularly high loss. More specifically, on one hand, energy is destroyed in view of the resistance caused by the axial impeller and, on the other hand, the drive of the axial impeller requires energy. A further disadvantage consists in that with the separation of ever finer material, the total power requirement of the separator and, above all, the energy requirement with regard to the finish sifted material increases considerably. Since a high degree of fineness of the separated material requires a low axial air velocity in the separating chamber, the resistance has to be correspondingly increased by the axial impeller. In other words, the axial impeller must rotate at high speed which in turn requires a higher power.

Still another drawback of the above referred to arrangement consists in that the material to be separated is charged into the separating chamber by means of a scattering This way of charging the material is not suitable to so disperse the material to be separated and, if necessary, also to disagglomerate the same as it is necessary for the subsequent separating process. Inasmuch as for a sharp separation of the material to be separated into fine material and coarse material it is indispensable to disperse the material to be separated as completely as possible which means to dissolve the clouds and strands of material to be separated into particles which are individually exposed to the separating air, the way of charging the material to be separated into the separating chamber is of particular importance. However, this task is carried out by a scattering dish only to a rather unsatisfactory extent. By means of a scattering dish, the material to be separated cannot even approximately be given the necessary radial velocity which would be required for properly spreading and dispersing the material to be separated over the entire free cross-section of the separating chamber. It can easily be shown that, in order to overcome the resistance which is'customary with industrial separators between the edge of the scattering 'dish and I the wall of the separating chamber, velocities would be necessary to which the particles of the material to be separated cannot be accelerated by a scattering dish of customary construction. In order to move radially, for instance, through a distance of one meter, while contrary to the actual facts it is assumed that the particles will not be interfered with by adjacent particles, it is necessary to impart upona particle having a diameter of 0.1 mm and a specific weight of 3.0 gr/cm a starting speed of more than 50 m/sec. For the still finer particles which, as a rule, make up the major percentage by weight of the material to be separated, a multiple of this speed is necessary for overcoming the assumed distance. This is hardly changed by the fact that the resistance of dust strands is less than the resistance of individual dust particles.

The assumption that the material to be separated is by means of a scattering dish spread like a veil over the free cross-section of the separating chamber is, therefore, erroneous. The radial velocity of the material to be separated will rather become zero after a short flight path, and the material to be separated first moves in the form of lumps and strands primarily in downward direction. The dispersing and sifting of the fine material is effected exclusively by the threedirnensional flow of the separating air prevailing in the separating chamber. With heretofore known air separators, this threedimensional flow, however, is not such, especially with regard to direction and magnitude, that the dispersion as well as'the separation can be carried out at a maximum effectiveness. The reason for this is seen in the introduction of the separating air into the separating chamber and in the design of the separating chamber.

The introduction of the separating air into the separating chamber is effected either by a circular cascade, usually louver, or in conformity with a more recent suggestion, by nozzles which are arranged below the scattering dish and which blow the separating air tangentially or axially into the separating chamber. Both types of introducing the separating air are disadvantageous.

When the separating air is introduced through a cascade, it will have in a desired manner a tangential and a radial speed component. Thus, in the separating chamber behind the cascade there will occur a more or less pronounced twist flow. Such rotation symmetric twist flow in a cylindrical pipe will always form a turbulent core, also called dead water core, in which no beneficial flow prevails but rather a considerable instability of the flow will be observed. This phenomenon is known in particular in connection with the construction of turboblowers or centrifugal blowers. All particles to be separated which due to the radial separating air component encounter a flow resistance which is greater than the centrifugal force acting upon the particles in view of the tangential separating air component will thus to a major extent reach the turbulent core of the vortex and will therefore practically not be subjected to the separating process. Instead they will to a greater extent remain in the vortex core and will here increase the dust accumulation until they drop into the discharge for the coarse material. With this arrangement it is particularly disadvantageous that in view of the described forces in particular the very fine particles, namely those which actually should remain in the separated material, are driven into the core of the vortex.

Incidentally, the diameter of the core of the vortex is exclusively dependent on the ratio between the axial and the tangential separating air velocity in the separating chamber and, more specifically, in such a way that with decreasing velocity ratio the diameter of the core of the vortex increases. Since the axial velocity of the separating air directly determines the degree of fineness of the separated material, an increase in the tangential velocity of the separating air at a predetermined fineness of the separated material as it is possible, for instance, with different types of air separators by changing the pitch of the blades of the cascade, will considerably increase the diameter of the core of the vortex. Although in this way the centrifugal force acting upon the particles is increased in view of the fact that the core of thevortex now begins already shortly behind the cascade, more and more particles of the desired separated material will pass into the core of the vortex. The desirable increase in the tangential component of the separating air in order to better the dispersion of the material to be separated will, therefore, bring about a poorer degree of separation. An increased dispersion of the material is particularly important when a fine material to be separated is involved, in other words, a material in which the axial separating air component is only short.

With air separators in which the blades of the cascade are not adjustable, the diameter of the vortex core remains constant because also the ratio of axial to tangential speed of the separating air is non-variable with eachcirculated quantity of air. However, at low air speeds, thus in particular when sitting fine material, the proportion of the particles of the desired separated material which will move into the vortex core will again increase because the radially inwardly directed flow resistance will with decreasing quantity of circulating air increase to a greater extent that the radially outwardly directed centrifugal force.

The fact that with increasing fineness, of the separated material the degree of separation decreases together with a decrease in the throughfiow of the finish separated material, has with heretofore known air separators its reason primarily in that the factors which unfavorably aflect the degree of separation add specific surface of approximately 5,000 cm'lgr, up to 50 percent of the charged material will pass through the separator unclassified.

Also when, in conformity with the above mentioned more recent suggestion, the separating air is introduced through tangential or axial nozzles into the separating chamber while the nozzles are connected to a pipe which leads coaxially into the separating chamber, the drawbacks of the customary cascades are not eliminated. There is rather encountered the drawback that the selected arrangement of the tangential nozzles makes possible neither a pronounced rotational flow or potential flow nor an axial separating air component which is uniformly distributed over the separator crosssection. As a result thereof, a strongly turbulent spacial flow will occur with a negative effect on the separating process. Definitely disadvantageous in this arrangement is the fact that the centrifugal force caused by the tangential separating air component drives the particles against the wall of the separating chamber where the major portion of said particles collects, slides downwardly and is thus withdrawn from the separating process. Inasmuch as the axial separating air component can become effective only beyond a certain distance from the tangential nozzles, all particles which reach the wall at a distance less than said last mentioned distance or which slip into this range from above will not be prevented from sliding into the discharge opening for the coarse material.

It is, therefore, an object of the present invention to provide an air separator which will overcome the above mentioned drawbacks and while requiring a small amount of power will have a high separating output which will remain constant even when the degree of fineness of the finish separated material is varied.

This object and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal section through an air separator according to the invention.

FIG. 2 represents a cross-section through the air separator of FIG. 1, said section being taken along the line II II.

The air separator according to the present invention which has a cylindrical separating housing with an inwardly located radial impeller or runner is characterized primarily in that a plurality of outside cyclones are by means of entrance passages arranged behind the radial impeller in such a way that not only the direction but also the magnitude of the absolute exit velocity of the separating air will not be changed during its entry into the entrance passages. The width of the cyclone passages directly ahead of the cyclones may be reduced by means of flaps built into said passages and being rotatable. The withdrawal of the separating air is effected by immersion tubes which extend into the cyclones and which are connected to the housing of the separating chamber by rectangular passages in such a way that the passages connected at an incline to the separating housing represent a cascade. Behind the stationary blades of the cascade there are provided adjustable blades which extend into the separating chamber while the angle formed by these blades with the circumference of the separating chamber may be varied at random. In the passages forming the cascade there are arranged flaps in such a way that by adjusting these flaps the exit cross-section of the passages can be made as small as desired. The housing for the separating chamber comprises a coaxial stationary pipe or tube which extends from the conical discharge opening for the coarse material to almost the cover disc for the radial impeller. Into this pipe, above the cascade, there is built a straight distributing cone the tip of which ends below the discharge end of a conveyor which is radially from the outside guided to the axis of the separator and which for purposes of passing the separating material and the coarse material therethrough has corresponding openings at different locations. By this construction of the separator according to the invention, all above referred to drawbacks and disadvantages of the heretofore known construction of air separators have been eliminated completely.

The decisive drawback that the diameter of the separating granules in the cyclones changes with the quantity of the circulated air, has been overcome in a simple manner by the fact that the entrance cross-section of the cyclones can be varied by an adjustment of the flaps in the cyclone passages in such a way that the diameter of the separated granules will remain constant. Inasmuch as for a given cyclone the end drop velocity of a granule having a certain separating diameter is, as mentioned above, directly inversely proportional to the quantity of air passing through the cyclone, and since on the other hand the end drop velocity of the separated granules monotonically increases or decreases with the ratio of the entrance cross-section to the cyclone cross-section, it is possible for each circulated quantity of air to select a cross-sectional ratio so that the separated granule end drop velocity remains constant. In other words, if, for instance, the circulated quantity of air is reduced because a finish separated material of a higher degree of fineness is to be processed, the entrance cross-sections of the cyclones are by pivoting the flaps in the cyclone passages reduced to such an extent that the desired separating granule diameter will be obtained. With the possibility created in this way to maintain the diameter of the separating granules or the separating output con- 'stant, also those described disadvantageous effects have been eliminated which are inherent to the return of fine finish material to the separating chamber.

The flow technically symmetric construction of the separator, i. e. the resistance which is practically the same for all flow threads, also assures that all cyclones will simultaneously be subjected to the flow of the separating air which fact in turn will result in an identical separating output for all cyclones.

The air separator according to the invention also eliminates the drawback of a high power consumption. The non-variable resistances inherent to the construction are small. On one hand, the path through which the separating air flows during a complete circulation is short and, on the other hand, the cyclones are so dimensioned that for a predetermined separating output they will cause only as minor a pressure loss as possible. The flowing of the separating air into the cyclone passages is accompanied by a particularly low resistance. Inasmuch as these cyclone passages are, in conformity with the present invention, connected behind the radial irnpeller in such a way that the absolute velocity of the separating air, after leaving the radial impeller, is not materially varied either with respect to its magnitude or its direction, the pressure loss inherent to this flow course is reduced to a minimum. In this connection it is also important that the exit twist of the separating air is practically not lost.

The variable resistance in the form of a counter running axial impeller will become completely superfluous with the air separator according to the invention. The change in the circulated quantity of air is effected by correspondingly changing the speed of the radial impeller. This will simultaneously bring about that the energy loss which is inherent to the change in the quantity of air will be of an absolute minimum value. It is a well known fact that the speed control of fans is most favorable from a standpoint of energy. Particularly important in this connection is the fact that the energy consumption with reference to the throughflow of the finish separated material varies with two and a half the power of the speed of the radial impeller. This means that in contrast to all heretofore known air separators the specific energy consumption decreases greatly with increasing fineness of the finish separated material.

The air separator according to the invention also is free from the drawbacks of the prior art which drawbacks are inherent to the introduction of the separating air into the separating chamber and to the charging of the material to be separated. While the introduction of the separating air also with the device according to the invention is effected through a cascade which is formed by those passages which connect the cyclones to the separating chamber, there is, however, the important difference that the magnitude as well as the direction of the separating air flowing into the separating chamber can be varied independently of each other. The absolute magnitude of the velocity of the separating air when entering the housing of the separating chamber is influenced by the flaps in the passages. When the exit cross-sections of the passages are reduced by pivoting the flaps or louvers, the entrance velocity of the separating air increases correspondingly. The change in the direction of the air entrance velocity is effected by means of the adjustable blades which extend into the separating chamber and which are mounted behind the stationary blades of the cascade, i. e. behind the passage walls. The velocity components of the twist flow behind the cascade may thus be varied to a great extent in conformity with size and direction and this may be effected independently of the respective quantity of circulated air.

This means that the twist flow can always be so adjusted that the core of the vortex which is unseparably connected with the twist flow has a diameter which is smaller than the diameter of the coaxial pipe in the interior of the separator chamber. In this way it is principally made impossible that the fine particles of the material to be separated will get into the core of a vortex and from the latter can pass to a major extent into the discharge member for the coarse material.

The charging of the material to be separated over the distributing cone is effected above the cascade in a range in which the twist flow has at least to a major portion the form of movement of a potential vortex. The material to be separated is afier leaving the distributing cone caught by the potential vortex and is radially distributed over the annular cross-section of the separating chamber while being dispersed to a major extent or disagglomerated. The dispersion and radial distribution are further aided by the fact that with a potential vortex the circumferential speeds are inversely proportional to the radii. Since in this way the velocities are different on two adjacent radii there is formed a kind of shear flow which aids the dispersion and disagglomeration. Furthermore, the material to be separated is immediately after leaving the distributing cone caught by a circumferential speed which has its maximum value at the outer circumference of the distributing cone and consequently considerably accelerates the material to be separated in a tangential and radial direction so that the material will in a desired manner quickly be moved out of the vicinity of the distributing cone and into the separating chamber. The independence of the twist flow from the circulated quantity of air additionally brings about the great advantage that it is possible to maintain constant the especially important circumferential speed at the marginal area of the distributing cone. This is of importance when sifting a fine material where the circulated quantity of air is very small.

With air separators according to the present invention it is, therefore, possible to maintain constant the diameter of the separating granules of the material separated in the cyclones and also the diameter of the vortex core as well as the circumferential speed of the twist flow at the distributing cone. This is realized by a corresponding actuation of three different flaps for each condition of operation.

If the values for the diameter of the separating granules, the diameter of the vortex core and the circumferential speed are given, there exists an unequivocal connection between the positions of the three flaps and the speed of rotan'on of the radial impeller. The automatic control of the flaps through corresponding adjusting means can, therefore, be effected in a simple manner by the corresponding speed of rotation of the radial impeller in such a way that the three above mentioned values remain constant for each circulated quantity of air.

The cylindrical configuration of the separating chamber of the air separator according to the invention also aids a situation which represents a further advantage. It is well known that the degree of separation at which a separator separates a dispersed material into a fine and a coarse material will be improved by a postsifting of a certain proportion of the fine material in the coarse material. Such post-sifting is effected in the air separator according to the invention in such a way that a relatively great portion of the coarse sifted material is subjected by the twist flow to centrifugal forces and above the cascade is rotated in the form of rings or strands and in this way is subjected to a continuous post-sifting.

The pronounced twist flow also brings about another advantage. It is well known that with each equilibrium separation in the separating chamber those particle's accumulate which have a diameter equalling the separating granule diameter. Consequently, the particles which are in equilibrium will move neither upwardly nor downwardly. This increase in the number of particles of approximately the same weight will, of course, bring about a decrease in the degree of separation of the separating process unless care is taken to remove these particles continuously from the separating chamber. The continuous removal of these particles is carried out in a simple manner by the twist flow. The particles of approximately the same weight are similar to all other particles in view of the rotation imparted thereupon and the centrifugal force inherent thereto driven toward the wall of the separating housing where they collect and are then subjected to the above mentioned post-sifting process.

The above described-possibility of maintaining constant or varying the diameter of the separating granules of the material separated in the cyclones by a corresponding adjustment of the flaps in the cyclone passages can be taken advantage of for influencing to a certain extent the granular structure of the finish separated material. A variation of the structure of the granules of the fine material is with all heretofore known air separators practically impossible. The resulting granular structure is rather dependent on the construction of the separator and on the separating principle. However, there exist instances in which the granular structure has a considerable influence on the quality of the fine material. For instance, it has been known for a long time that for the strength of cement the granular structure of the cement powder is of great importance. In such instances where the requirement for a certain granular structure supersedes the requirement for as fine a degree of separation as possible, it is possible with a separator according to the invention to approximately obtain the desired granular structure of the fine material by a different adjustment of the flaps in the cyclone passages. In this way, there is deposited or collected in each cyclone a fine material with a different granular structure, and the granular structure of the total fine material which is composed of as many different granular structures as there are cyclones is thus variable to the desired extent.

Referring now to the drawings in detail, it will be noted that above a cylindrical housing 1 of a separating chamber there is arranged a radial impeller 2 which is adapted through the intervention of a transmission 3 to be driven by a speed variable motor 4. Behind the radial impeller 2 there are provided entrance passages 5 to cyclones 6. Installed in each of these entrance passages 5 and parallel to the outer vertical passage wall is a flap 7 which is adapted by means of an adjusting member 8 to be tilted in such a way that the entrance cross-section of the cyclones 6 can be varied from a maximum value to zero and vice versa.

The cyclones 6 are adapted to communicate with the separating chamber defined by the housing 1 through immersion pipes 10 introduced into the exit passage 9 from below for the fine material and by passages 11 communicating with the immersion pipes 10, the side walls of the passages 11 forming a cascade confined by the circumference of the housing 1. Arranged behind the stationary blades formed by the side walls of the passages 11 are movable blades 12 which by means of an adjusting member 13 adapted to bring about a rotary movement can be so adjusted that each desired pitch or angle of the blades 12 with the circumference of the housing 1 may be obtained. Built into the passages 11 are flaps 14 which extend parallel to the upper inclined side walls and which can likewise be adjusted by means of an adjusting member 15 in such a way that the magnitude of the exit cross-section of the passages 11 can be varied from a maximum value to zero and vice versa in an infinitely fine manner.

Built into the housing 1 is a coaxial pipe 16 which rests on a conical discharge member 17 for the coarse material. The passage of the coarse material from the circular separating chamber to a discharge 18 is made possible by openings 19. At the upper portion of the coaxial pipe 16 there is provided a distributing cone 20 located above the cascade and having its tip extend to an area below the outlet of an air conveying duct or trough 21. Through openings 22 the material to be separated passes from the distributing cone 20 into the separating chamber. Above the openings 22 the coaxial pipe 16 continues and ends directly below the cover disc of the radial impeller 2.

The air separator according to the present invention operates as follows: The material to be separated passes through the air conveying duct 21 into the interior of the coaxial pipe 16 where it drops upon the tip of the distributing cone 20 on which it is uniformly distributed and due to the inclination of the distributing cone 20 slides through openings 22 into the separating chamber. lrnmediately after entering the separating chamber, the material to be separated is caught by the here rotating potential vortex which is generated by the separating air entering through the passages 11 and, as the case may be, by a corresponding adjustment of the flaps l4 and blades 12. The material to be separated is in this way accelerated tangentially and radially and is Y thus uniformly distributed over the entire circular cross-section of the separating chamber. During this operation during which the material to be separated is dispersed to a considerable extent and, as the case may be, is also disagglomerated, there is simultaneously effected the separating process proper which is based on the principle of equilibrium sifting. The vertical separating air velocity which is independent of the potential vortex and is infinitely variable by a corresponding selection of the speed of rotation of the radial impeller 2 carries vertically upwardly all the particles having a weight less than the resistance exerted upon said particles by the vertical separating air velocity. The particles the weight of which exceeds the said resistance drop downwardly into the discharge element 17 for the coarse material, and the latter leaves the discharge element 17 through the outlet 18.

The upwardly carried particles of the fine material first enter the radial impeller 2 and from the latter pass into the inlet passages 5 and thereupon into the cyclones 6. In the cyclones 6 the fine material is separated in a known manner with the exception of an unavoidable remainder. This remainder is kept as small as possible by pivoting the flaps 7, if necessary, in the entrance passages 5 so as to set the same for the smallest possible diameter of the separating granules. The fine material finally leaves the cyclones 6 through the outlets 9 which, for instance, lead into a circular air duct which is located below the outlets 9 and which collects the fine material and transports it away.

It is, of course, to be understood that the present invention is, by no means, limited to the particular structure shown in the drawings but also comprises any modifications within the scope of the appended claims.

What I claim is:

l. A circulating air separator with a closed circuit path for separating air which includes: housing means substantially cylindrical over the entire length thereof and having a distributing cone located centrally therein by way of which separating material is centrally supplied while defining separating chamber means therewith where separation of separating material occurs into coarse material and fine material by way of separating air based upon equilibrium principle, an internal radial impeller means arranged at the upper end portion of said separating chamber means above said distributing cone, motor means drivingly connected to mersion pipe means extending into the lower portion of said cyclones, and additional conduit means establishing communication between said immersion pipe means and the lower portion of said separating chamber means, said additional conduit means being connected angularly adjacent said housing means forming a cascade.

2. An air separator according to claim 1, in which said cascade is stationary, and which includes movable blades extending into said separating chamber means,

' said blades being adjustable so as to form different angles with regard to the circumference of said separating chamber means.

3. An air separator according to claim 1, in which control means formed by flap. means which are pivotally mounted in said inlet conduit means of said cyclones and operable selectively to vary the effective cross-section through which said inlet conduit means communicate with said cyclones, said flap means being adjustable from a minimum cross-sectional value to a maximum value thereof and vice versa.

4. An air separator according to claim 3, which includes additional flap means arranged within said additional conduit meam and operable for selectively varying and controlling the free cross-section establishing communication between said additional conduit means and said separating chamber means. a 5. An air separator according to claim 3, which includes conical discharge means connected to the lower end of said housing means, pipe means substantially coaxially arranged fixedly within said housing means and in radially spaced relationship thereto, said pipe means extending from a portion of said conical discharge means into the vicinity of said radial impeller meam, said distributing cone communicating with openings in said pipe means at a level intermediate said impeller meam and said cascade, andconveying means leading radially from the outside into said housing means and ending above said distributing cone, said pipe means being provided with opening means for passing coarse material and separated material to be withdrawn from the separator through said opening means.

6. An air separator according to claim 3, in which said control means also include additionally flap means arranged in said additional conduit means, said sep'arator also including adjusting means operatively .conf sfifl l jl l l ller m or co r i t rfili g s id fi g means to maintain substantially constant the diameter of the finish separated granules, the diameter of the vortex and the circumferential speed of the twist flow on the outer marginal area of the distributing cone.

I i l 

1. A circulating air separator with a closed circuit path for separating air which includes: housing means substantially cylindrical over the entire length thereof and having a distributing cone located centrally therein by way of which separating material is centrally supplied while defining separating chamber means therewith where separation of separating material occurs into coarse material and fine material by way of separating aIr based upon equilibrium principle, an internal radial impeller means arranged at the upper end portion of said separating chamber means above said distributing cone, motor means drivingly connected to said impeller means for rotating the same, a plurality of cyclones arranged outside said separating chamber means, inlet conduit means interconnecting said cyclones with said separating chamber means and leading in the direction of absolute exit velocity of separating air behind said radial impeller means so that both the direction and also the magnitude of the absolute exit velocity of the separating air during entry into said inlet conduit means experience no alteration, and immersion pipe means extending into the lower portion of said cyclones, and additional conduit means establishing communication between said immersion pipe means and the lower portion of said separating chamber means, said additional conduit means being connected angularly adjacent said housing means forming a cascade.
 2. An air separator according to claim 1, in which said cascade is stationary, and which includes movable blades extending into said separating chamber means, said blades being adjustable so as to form different angles with regard to the circumference of said separating chamber means.
 3. An air separator according to claim 1, in which control means formed by flap means which are pivotally mounted in said inlet conduit means of said cyclones and operable selectively to vary the effective cross-section through which said inlet conduit means communicate with said cyclones, said flap means being adjustable from a minimum cross-sectional value to a maximum value thereof and vice versa.
 4. An air separator according to claim 3, which includes additional flap means arranged within said additional conduit means and operable for selectively varying and controlling the free cross-section establishing communication between said additional conduit means and said separating chamber means.
 5. An air separator according to claim 3, which includes conical discharge means connected to the lower end of said housing means, pipe means substantially coaxially arranged fixedly within said housing means and in radially spaced relationship thereto, said pipe means extending from a portion of said conical discharge means into the vicinity of said radial impeller means, said distributing cone communicating with openings in said pipe means at a level intermediate said impeller means and said cascade, and conveying means leading radially from the outside into said housing means and ending above said distributing cone, said pipe means being provided with opening means for passing coarse material and separated material to be withdrawn from the separator through said opening means.
 6. An air separator according to claim 3, in which said control means also include additionally flap means arranged in said additional conduit means, said separator also including adjusting means operatively connected to said flap means and responsive to the speed of said radial impeller means for controlling said flap means to maintain substantially constant the diameter of the finish separated granules, the diameter of the vortex and the circumferential speed of the twist flow on the outer marginal area of the distributing cone. 